The invention relates to a method of producing chromium (III)-N-acylanthranilates for dispersions for applying solid particles to surfaces by electrophotographic means.
German application No. 24 60 763 discloses a dispersion for electrophotographically applying solid particles to surfaces, which dispersion comprises, besides the solid particles an apolar dispersion agent, a non-ionogenic macromolecular compound which is soluble in the dispersion agent and a charge-controlling material which controls charging of the solid particles. The dispersion comprises as the single charge-controlling material a chromium-(III) salt of the formula Cr(AN).sub.n (OH).sub.3-n, wherein n= 1, 2 or 3 and AN represents the residual acid of an anthranilic acid which may be substituted in the benzene nucleus, and whose amino group is acylated with a fatty acid of 6 to 20 carbon atoms, In the formula n is preferably equal to 1 or 2. The acylated anthranilic acid may be substituted in the nucleus by halogen, aryl-, alkyl-aralkyl-, nitro-, amino-, O-alkyl-, O-aryl-, O-aralkyl-, hydroxyl-and/or ester groups. The amino group of the possibly substituted anthranilic acid is preferably acylated with a stearoyl group or a lauroyl group or an oleoyl group.
German application No. 21 16 556 discloses the preparation of chromium (III) salts of stearoyl anthranilic acids as, via a Schotten-Baumann condensation of anthranilic acid with stearoyl chloride to form stearoyl anthranilic acids. The sodium salt of these acids are converted in an aqueous solution with chromium (III) sulphate into chromium tris-stearoyl anthranilate, which is precipitated from the aqueous solution in the form of a green precipitate. After the usual washing and drying operation, the salt readily dissolves in hydrocarbon solvents. When used as control material in the above-mentioned dispersions the chromium (III)-N-acyl anthranilates produced in an aqueous solution have the disadvantage that the precipitate of the chromium compound is greatly contaminated with free acids (stearoyl anthranilic acid).
In accordance with German patent application 2460763 corresponding to U.S. Pat. No. 4,024,084 the chromium (III)-N-acyl anthranilates are produced in a methanol solution from N acyl anthranilic acids and Cr(NO.sub.3).sub.3. 9H.sub.2 O in the required ratios by the addition of the methanolic solution of CH.sub.3 ON methanol. The resulting precipitate is separated from the methanol by decanting, washed several times with methanol and dissolved again in toluene or chloroform or tetrahydrofuran. The solution is filtered and evaporated to dryness. The composition is checked by determining the chromium content. Standard solutions having a given concentration are produced for the production of the dispersions. Toluene, xylene, benzene, ethanol, propanol, butanol and other alcohols, dimethylformamide, dimethylsulphoxide, pyridine, acetonitrile, chloroform and other halogenized hydrocarbons may, for example, be used as solvents. The solvents may also contain small quantities of water.
A problem in the production of chromium (III)N-acylanthranilates is to produce the materials reproduceably in a simplest possible manner. It appeared, for example, that problems are encountered in the evaporation of toluene; there is a great difference in the properties of the chromium anthranilates obtained depending on the fact of whether the distillation of toluol has been done very thoroughly or not.